1. Field of the Invention
This invention is concerned with a V-type two cycle internal combustion engine which has scavenging ports opening into cylinders and is equipped with a mechanical supercharger having a set of rotors.
2. Description of Related Art
Typically, reciprocal engines have intake ports which are formed in the cylinder head so as to open into cylinders. However, intake ports of two cycle engines are formed in the cylinder block so as to open into cylinders. For instance, Japanese Unexamined Patent Publication No. 62-135655 describes a two cycle engine in which scavenging ports are formed, as intake ports, in the cylinder block so as to open into cylinders. Following combustion, when the piston reaches the bottom dead center of a combustion stroke, fresh air is introduced through the scavenging ports and, at the same time, expels and pushes out burned gases into the exhaust ports.
In this instance, two cycle engines are often realized in V-type engines having two, i.e. left and right, cylinder banks. Such a two cycle V-type engine is equipped with a mechanical supercharger which has a set of rotors to supercharge intake air. In this instance, the supercharger is installed between the left and right cylinder banks of the engine, and a surge tank, which communicates with the scavenging ports, is displaced downstream the supercharger between the left and right cylinder banks. In this arrangement, if both rotors of the mechanical supercharger are lined up horizontally side by side, then, because of the structure of the mechanical supercharger, the air discharge opening formed in its housing faces upward. This leads to unavoidably increasing the overall height of the engine. In order to lower the overall engine height, the mechanical supercharger may be set up so that both rotors are aligned vertically, and then it may be lowered down so as to situate its top close to the bottom of the V-shaped space between the cylinder banks. However, such an arrangement of the mechanical supercharger causes the air discharge opening formed in one side wall of the housing to be blocked by one of the cylinder banks, and reduces the capacity of the surge tank which is also situated below the mechanical supercharger.